The present invention relates to a safety device for electrical control apparatus having a first member disposed in an opening in a second member, where the first and second members are adapted and arranged for relative movement with respect to each other, and in particular for a movable member which is reciprocably movable in a longitudinal direction in an opening in a stationary member. The invention is particularly suited for electrical control apparatus such as dimmer switches for controlling the intensity of lights of the type which utilize a linearly moving control member attached to a linear potentiometer. The control member typically projects through an elongated slot in an escutcheon plate.
In dimmer switches of this type, it is obviously necessary that the control member be permitted to move freely in the opening. This necessitates keeping the opening unobstructed. However, in many applications, there exists the danger that foreign objects can enter the open portions of the opening around the control member. For example, someone could inadvertently or deliberately insert a metallic object through the slot and contact live electrical components of the dimmer switch. Such an occurrence could result in serious injury to the person, as well as damage to the lighting system.
In fact, some standards agencies have long recognized this problem and have taken steps to prevent such occurrences. With respect to dimmer switches, British Standards Institution Specification No. BS5518:1977 requires that dimmer switches shall be constructed such that there are no free openings in their enclosures when they are fixed and wired as in normal use.
Previous attempts have been made to solve the problem of covering the open portions of the opening while allowing the control member unrestrained movement in the opening. One solution involves the use of a large sliding member coupled to the control element to cover the opening. An example of such a structure is shown in U.S. Pat. No. 3,746,923. There, a large rectangular opening is provided in the escutcheon plate and a slide member is inserted into the opening from behind the plate. The slide member has twice the area of the opening so that the opening is covered by the slide member at all times. The slide member is movable with the dimmer's linearly moving control member, and must be made at least twice as long as the rectangular opening to ensure that the opening is covered at all times, no matter what the position of the control member. Thus, a great deal of extra space above and below the opening is required.
Another solution involves the use of a continuous belt of flexible material wrapped around the housing of the dimmer switch to block the opening. A small hole is made in the belt to receive the control member. The belt is continuous and moves with the control member so that the slot is always covered no matter how the control member is moved.
The first solution requires a great deal of area, making dimmer switches which use that solution larger than they need to be. The second method requires the mechanism to be located on all sides of the dimmer switch. This can cause component layout and interference problems.
There is a need for a safety device which overcomes the disadvantages of previous safety devices. The present invention provides such a device. In addition, the present invention requires only a minimal amount of extra space above and below the opening, and enhances the "feel" of the dimmer switch mechanism employing the safety device of the invention.